Lealiifano started his first Test in three years against Argentina last month after a cancer battle, while O'Connor will begin his first international since 2013 against the All Blacks in Perth on Saturday.
Both players were experienced campaigners before their hiatus from the Wallabies, and have slotted back in seamlessly.
Hooper said Lealiifano, the Brumbies captain who has retained his place at flyhalf at the expense of Bernard Foley, had proved to be a major asset.
"He's really calm, collected. He simplifies things really nicely, he's in a really good place with his rugby at the moment," he said.
"He's a real calming influence on the team and in a game of high emotion, it's good to bring everyone back down and get their eyes on the job."
O'Connor started his last Test in 2013 before a series of off-field indiscretions saw him fall out of favour. He came off the bench against Argentina, but starts against New Zealand in the Bledisloe Cup clash, which also doubles as a Rugby Championship match.
Hooper said he had full confidence in the utility back.
"He's really, really excited I think. He's been doing all the stuff that he needs to do to get on the field," he said.
"He's played in these games before and done really well in these games before. I'm sure he'll be calling on that and other things he's learned over the past few years.
"Like Christian, he's got a good calming influence. I certainly trust him fully in his ability and his temperament," he added.
Scrum-half Nic White, preferred to veteran Will Genia against New Zealand, is another experienced player back in the frame after missing several years of Wallabies' action by playing in Europe.
Hooper said all three had stepped back in with little fuss.
"I believe that being away from the set-up, the Test arena, you come back in so hungry and so excited to get back on the field," he said.
"And that's not just an individual thing, it rubs off on the guys directly around them. The competition and the open discussion that has brewed within the team has been really positive for us this year."
15 Kurtley Beale, 14 Reece Hodge, 13 James O'Connor, 12 Samu Kerevi, 11 Marika Koroibete, 10 Christian Lealiifano, 9 Nic White, 8 Isi Naisarani, 7 Michael Hooper (captain), 6 Lukhan Salakaia-Loto, 5 Rory Arnold, 4 Izack Rodda, 3 Allan Alaalatoa, 2 Tolu Latu, 1 Scott Sio
Substitutes: 16 Folau Fainga'a, 17 James Slipper, 18 Taniela Tupou, 19 Adam Coleman, 20 Luke Jones, 21 Will Genia, 22 Matt Toomua, 23 Tom Banks
15 Beauden Barrett, 14 Ben Smith, 13 Jack Goodhue, 12 Anton Lienert-Brown, 11 Rieko Ioane, 10 Richie Mo'unga, 9 Aaron Smith, 8 Kieran Read (captain), 7 Sam Cane, 6 Ardie Savea, 5 Sam Whitelock, 4 Scott Barrett, 3 Owen Franks, 2 Dane Coles, 1 Joe Moody
Substitutes: 16 Codie Taylor, 17 Atu Moli, 18 Angus Ta'avao, 19 Patrick Tuipulotu, 20 Matt Todd, 21 TJ Perenara, 22 Ngani Laumape, 23 George Bridge